The present invention generally relates to head carriage mechanisms of a magnetic disk recording/reproducing apparatus recording and/or reproducing information on and from a flexible magnetic disk, and more particularly to a reliable head carriage mechanism for such an apparatus having a simple structure.
Generally, a magnetic disk recording/reproducing apparatus records and/or reproduces an information signal on and from a flexible magnetic disk using a head carriage mechanism on which a magnetic head is mounted.
Conventionally, such a head carriage mechanism has a construction in which a head carriage carrying a magnetic head is supported slidably on a pair of parallel guide rods and the moving plane or plane of transportation of the head carriage is made parallel to the recording plane of the magnetic disk When the magnetic head is transported along a recording track on the disk, the head carriage is moved along the guide rods by a drive system such as a stepping motor.
However, such a structure has a problem in that accurate positioning of the head carriage, which has to be established in order to maintain the moving plane of the head carriage at a designed predetermined position, is difficult. Because of this reason, the adjustment inevitably becomes complicated and delicate, and requires a large number of parts.
In order to avoid such a problem as well as to reduce the cost, U.S. Pat. No. 4,428,012 or Japanese Laid-open Patent Application No. 61-5481 discloses a structure using a single guide rod on which the head carriage is held slidably. In order to maintain the head carriage at a predetermined plane during the transportation of the head carriage, a pressing mechanism including a resilient member is provided so as to act between the head carriage and a base mount such as a frame or chassis of the apparatus on which the head carriage is mounted. In such a mechanism, however, it is difficult to maintain the pressing force exerted by the resilient member of the pressing mechanism uniform throughout the entire range of movement of the magnetic head As a result, frictional wear takes place at the part where the head carriage or the base mount makes a sliding engagement with the pressing mechanism. Such wear changes the position of the moving plane of the magnetic head. It will be easily understood that such a deviation in the moving plane of the magnetic head increases with increasing time.
Further, the pressing mechanism aforementioned uses a number of parts such as the resilient member, lever member, roller and various bearings to support the lever member of the roller, and therefore has a problem in that the structure is complex and the assembling work is difficult.
Furthermore, such a pressing mechanism is usually mounted on the head carriage as is disclosed in the Japanese Laid-open Patent Application No. 61-5481. In such a structure, the pressing mechanism is moved together with the movement of the head carriage. Thus, there arises another problem in that the state of engagement of the engaging part where the pressing mechanism and the base mount make a contact tends to be changed.
The structure in which the pressing mechanism is mounted on the base mount as is disclosed in the U.S. Pat. No. 4,428,012 is more advantageous in terms of the stabilization of the state of the engaging part than the structure in which the pressing mechanism is mounted on the head carriage. However, there is a problem in that the urging action depends rather sensitively on the temperature change in various parts of the apparatus. Such a temperature change may occur as a result of the heat of the stepping motor, for example. Because of this reason, it becomes necessary to provide an additional device to compensate for the temperature change in the structure. However, such a device complicates the structure of the head carriage mechanism.